1. Field of the Invention
The present invention relates to a pyrolytic boron nitride double container suitable for containing a material serving as a source of molecular beams used in molecular beam epitaxy (hereinafter abbreviated as “MBE”).
2. Description of the Related Art
MBE is one method of manufacturing thin film, in which a thin-film growth chamber is maintained at ultra-low vacuum of 10−6-10−11 Torr; a container that contains a material serving as a molecular beam source is heated to, for example, a temperature of 500-1500° C.; and molecular beams generated from the melt material are caused to impinge onto a heated substrate, so that a layer having a thickness corresponding to a few atoms is formed on the substrate in a controlled manner. Especially, the MBE method has been widely used for manufacture of epitaxial film of compound semiconductors such as GaAs, and from the viewpoints of purity, heat resistance, strength, and the like, a pyrolytic boron nitride (PBN) container made through chemical vapor deposition (hereinafter abbreviated as “CVD”) has been widely used as a container for containing a material serving as the molecular beam source.
Conventionally, in such an MBE method, the temperature of a material is increased to generate molecular beams of the material. Then, after an epi-layer is grown, on-off control action of the beam is performed with shutter when the operation is suspended for a short time. Meanwhile in case of the suspension for many hours the temperature of the material is lowered, and in an emergency such as electric power failure it is lowered as well. And when the operation is restarted, the temperature of the material is increased again.
At this time, the rise and drop in the temperature of the material metal causes its expansion, shrinkage, solidification expansion, or solidification shrinkage to thereby generate a stress in the container, with the result that the container may break. If the material melt leaks out of the container, the material melt adheres to a heater, other heating members, and members inside a furnace, resulting in corrosion, degradation, and/or breakage of these components and members; and/or short-circuit of the heater.
In order to prevent such breakage of the container, there has been proposed a pyrolytic boron nitride container composed of double or multiple layers which are connected to each other with low bond strength. In this method, the container has a resistance to the shrinkage of the material melt, however when the material expands largely, this method has been ineffective frequently.
In order to solve the above-described problems, there has been conceived a double container which has some amount of space between the inner container and the outer container. However, in this case, some drawbacks are likely to occur, for example, heat conduction and heat efficiency for heating the inner container are not good, the temperature is unstable, and so forth.